DOMINANT FREQUENCY-ANALYSIS OF EEG REVEALS BRAINS RESPONSE DURING INJURY AND RECOVERY

A new method of monitoring and analyzing electroencephalogram (EEG) si gnals during brain injury is presented, EEG signals are modeled using the autoregressive (AR) technique to obtain the frequencies where ther e are peaks in the spectrum, The powers at these dominant frequencies are analyzed to reveal the state of brain injury during an experimenta l study involving progressive hypoxia, asphyxia, and recovery, Neonata l piglets (n = 8) were exposed to a sequence of 30 min of hypoxia (10% oxygen), 5 min of room air, and 7 min of asphyxia, They then received cardiopulmonary resuscitation and were subsequently monitored for 4 h , An optimal AR model order of six was obtained for these data, result ing in three dominant frequencies, These dominant frequencies, referre d to as the low, medium, and high frequency components, fell in the ba nds 1.0-5.5 Hz, 9.0-14.0 Hz, and 18.0-21.0 Hz, respectively. A remarka ble feature of our data is the spectral dispersion, or diverging trend s in the three frequency bands. During hypoxia, the relative powers of the medium and high-frequency components of EEG increased up to 160% and 176%, from their respective baseline values, During the first minu te of asphyxia the medium- and high-frequency powers (relative to base line) increased by 280-400%. The power in all three frequency componen ts went down to nearly zero within 40-80 s of asphyxia, During recover y, the phenomenon of burst-suppression was clearly exhibited in the lo w-frequency component. A new index, called mean normalized separation, representing the degree of disproportionality in the recovery of powe rs of the three dominant components relative to their mean recovered p ower, is presented as a possible single indicator of electrical functi on recovery. In conclusion, dominant frequency analysis helps reveal t he brain's graded electrical response to injury and recovery.